The operative principle of reverse osmosis systems consists in guiding the water to be prepared in a filter module under high pressure along the surface of a semipermeable membrane, with part of the water, the so-called permeate, passing through the membrane and being collected at the other side of the membrane and supplied to the consumption points. The part of the raw water that does not pass through the membrane and is enriched with retained substances, the so-called concentrate, flows at the end of the flow path of the primary chamber out of the membrane module.
As a typical example, the diagram shown in FIG. 1 illustrates the cooperation of essential functional elements of a reverse osmosis system according to the prior art. The raw water to be prepared flows out of the feed line 1 and via the valve 4 into a buffer vessel 5 with installed fill level control. The water passes out of the container 5 through the line 17 via the pump 6 into the reverse osmosis filter 7, the primary chamber 9 of which is separated by the semipermeable membrane 10 from the secondary chamber 8. The permeate flows out of the secondary chamber 8 into a ring line 15/16 from which the consumer lines 13 are branched off. At the end of the ring line, permeate produced in excess can flow via an inserted pressure holding valve 14 back into the vessel 5, the setting of said valve determining the pressure prevailing in the ring line 15/16.
The pressure that is needed for filtration and is prevailing in the primary chamber of the RO filter 9 is produced by the pump 6 in combination with a flow resistance means 11, e.g. in the form of a throttle valve or a pressure valve, which is inserted into the concentrate line 18 downstream of the filter.
The concentration difference of retained substances between outlet and inlet of the primary chamber 9 is of great importance to the function of the RO filter 7. At an excessively high concentration, particularly of calcium and magnesium, there is an increased risk that these constituents exceed a critical limit. The permeability of the membrane 10, and thus the permeate flow, will then decrease due to the formation of deposits, which means that the reverse osmosis filter will become useless prematurely.
Due to this fact especially the calcium and magnesium salts have so far been exchanged in consideration of the raw water quality by the upstream cation exchanger columns 2 for sodium. Ion exchangers are maintenance- and cost-intensive.
Sodium chloride and flushing water are needed for the reliable operation of the cation exchangers. Moreover, salt has to be refilled manually at regular intervals. In addition, the salt-containing flushing water contaminates the waste water.
Reverse osmoses serve particularly to obtain sterile water.
The part of the supplied tap water that does not pass through the membrane 10 and is enriched with retained chemical water constituents and bacteria will form a biofilm on the inner surfaces of the liquid-conducting system. The excretions of the biofilm may pass as pyrogens and endotoxins through the non-ideal membrane 10 and may contaminate the high-purity permeate circuit 15/16.
Therefore, it has so far been customary to carry out a thermal or chemical disinfection on reverse osmosis systems at regular intervals. To this end the operation is interrupted and thermal energy or chemical disinfectants are supplied to the system.
Due to the high risks that are particularly posed by chemical disinfection, the work steps have here to be monitored manually. This normally means considerable work.